Several environmental campaign groups are urging people to take fewer flights for the sake of the global climate.

They say aircraft emit more of the main greenhouse gas than cars for each passenger they carry.

The groups say one return flight from the United Kingdom to Florida produces as much carbon dioxide (CO2) as a year's driving by the average British motorist.

And they say commercial jets add almost as much to global warming annually as the whole of Africa.

The groups are Friends of the Earth, the Aviation Environment Federation, the National Society for Clean Air, and the Heathrow Association for the Control of Aircraft Noise.

In a report, Aviation and Global Climate Change, they say:

air travel produces 0.17 kg of CO2 per km travelled for each passenger, against 0.14 kg/km for car travel

a return flight from London to Miami (14,207 kms) produces 2,415 kg of CO2 per passenger, more than the 2,255 kg produced annually by the average British motorist's 16,108 km

the world's 16,000 commercial jet aircraft produce more than 600 million tonnes of CO2 annually, almost as much as the entire African continent

the number of people flying is expected almost to double in the next 15 years

many tourist destinations could be submerged by rising sea-levels caused by climate change

because airlines do not pay tax on the kerosene they use as fuel, they do not have an incentive to save it or to fill every seat on their planes.

Friends of the Earth wants people to think about spending their holidays closer to home, to reduce the length of time they spend in the air.

It also recommends taking trains instead of using aircraft for short distances, and says teleconferencing could replace inessential business flights.

Hugh Somerville, of British Airways, said he thought the report's figures on aircraft fuel efficiency were "a gross overestimate".

Efficiency doubled

He told BBC News Online: "The fuel efficiency of our fleet has doubled in the last 20 to 25 years, and we are getting results which produce about 30% or 40% of the CO2 the report mentions.

"Nevertheless, we take this problem very seriously, and we share the groups' concerns.

"We are sponsoring a study on emissions trading, which we think will probably be the best way to deliver improvements by aviation.

"And we are involved with work at the International Civil Aviation Organisation that's looking at market options for improving fuel efficiency."

Some scientists remain unconvinced of the reality and urgency of climate change, and say our understanding of climate processes is still very limited.

Awaiting proof

They believe the evidence that human activities are inducing rapid change is weak.

They highlight the inconsistencies between the temperature records taken at the Earth's surface, which show rapid warming over the last two decades, and the data produced by satellite and balloon studies.

These show little or no warming higher in the atmosphere over the same period.